1. Field of the Invention
The present invention relates to a substrate treatment system, a substrate transfer system, and substrate transfer method for use in transferring a substrate such as a semiconductor wafer and an LCD substrate from a cassette station to a process station.
2. Discussion of the Background
Recently, sizes of semiconductor wafers have been increased. With the size increase, the wafers tend to be processed one by one in semiconductor device manufacturing processes. For example, in a complex process system (resist coating and developing are performed in one process), substrates are taken out from a cassette one by one, processed in a process unit, and returned to the cassette one by one.
In a conventionally-used coating and developing process system as shown in FIG. 1, a plurality of cassettes CR are placed on a cassette station 102. Wafers W are taken out from the cassette CR one by one by means of a wafer transfer mechanism 105, loaded into a process station 101, and subjected to a resist coating and developing process. The wafer transfer mechanism 105 comprises a movement unit 103 and an arm 104. The arm 104 is moved separately by means of the movement unit 103 in the X, Y, and Z axis directions and rotated about the Z axis by a .theta. angle. The processed wafer W is returned to the cassette CR on the cassette station 102 by the wafer transfer mechanism 105.
To prevent particles from attaching onto the wafer W, the resist coating and developing process system is positioned in a clean room where clean air constantly flows downwardly.
Furthermore, to prevent particles from entering the cassette CR during the conveyance of the cassette, a detachable cover is provided to the opening of the cassette CR. However, when the cassette CR is placed in the cassette station 102 with the cover removed, the cover intervenes in the down-flow of clean air in the process system, creating an air flow which will allow invasion of particles into a process station 101.
In the wafer processing step, a washing device (scrubber) is used for washing the front and rear surfaces of the wafer with a brush. The washing device comprises a cassette station 401 and a process station 402. The process station 402 comprises a center transfer passage 420, a front-surface washing unit 421, a rear-surface washing unit 423, wafer reverse units 427, 428, heating and cooling units 425, 426, and a wafer transfer mechanism 403.
To prevent particles from attaching to the wafer as much as possible in such a washing device, the wafer cassette CR is placed in an airtight chamber (So-called SMIF POD) 413 and the SMIF POD containing the cassette CR is transferred to the cassette station 401. In the cassette station 401, the SMIF POD 413 is descended to the wafer transfer portion while the SMIF POD 413 is kept airtight. In the SMIF system, wafers are transferred one by one from the cassette CR of the wafer transfer portion to the process station 402, washed, and returned to the cassette CR. Thereafter, the wafer cassette CR is ascended and returned to the SMIF POD 413 on the cassette station 401.
However, the conventionally-used device has a problem. If a wafer W protrudes from the cassette CR, the protruding wafer sometimes hits against the upper wall of the wafer transfer portion and causes damages when the wafer cassette CR is returned to the SMIF POD 413. Furthermore, when the wafer protrudes from the cassette CR, the protruding wafer interferes with a mapping sensor 21b, inducing misoperation of mapping, as shown in FIG. 9.